1. Field of the Invention
The present invention relates generally to ink-jet printing and, more specifically to an ink-jet pen carriage assembly having a torsional deflection control pen latching subsystem for increasing stiffness and maintaining accurate pen-to-paper alignment.
2. Description of Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
FIG. 1 depicts a hard copy apparatus, in this exemplary embodiment a computer peripheral, ink-jet printer, 101. A housing 103 encloses the electrical and mechanical operating mechanisms of the printer 101. Operation is administrated by an electronic controller 102 (usually a microprocessor or application specific integrated circuit (xe2x80x9cASICxe2x80x9d) controlled printed circuit board) connected by appropriate cabling to a computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions and logic with firmware or software instructions for conventional or general purpose microprocessors or with ASIC""s. Cut-sheet print media 105, loaded by the end-user onto an input tray 120, is fed by a suitable paper-path transport mechanism (not shown) to an internal printing station, or xe2x80x9cprint zone,xe2x80x9d 107 where graphical images or alphanumeric text is created. A carriage 109, mounted on a slider 111, scans the print medium. [Stationary, page-wide, ink-jet printhead arrays are also known in the art; page-size printhead arrays are contemplated.] An encoder subsystem 113, 114 is provided for keeping track of the position of the carriage 109 at any given time. A set of individual ink-jet pens, or print cartridges, 115X is mounted in the carriage 109 (described in more detail hereinafter with respect to FIG. 2B). Generally, in a full color system, inks for the subtractive primary colors, cyan, yellow, magenta (X=C, Y, or M) and true black (X=K) are provided; in some implementations an ink-fixer chemical (X=F) is also used. An associated set of replaceable or refillable ink reservoirs 117X is coupled to the pen set by ink conduits 119. Once a printed page is completed, the print medium is ejected onto an output tray 121. The carriage scanning axis is conventionally designated the x-axis, the print media transit axis is designated the y-axis, and the printhead firing direction is designated the z-axis.
For convenience of describing the ink-jet technology and the present invention, all types of print media are referred to simply as xe2x80x9cpaper,xe2x80x9d all compositions of colorants are referred to simply as xe2x80x9cink,xe2x80x9d ink-jet writing instruments are referred to as xe2x80x9cpensxe2x80x9d or xe2x80x9ccartridges,xe2x80x9d and all types of hard copy apparatus are referred to simply as a xe2x80x9cprinter.xe2x80x9d No limitation on the scope of invention is intended nor should any be implied.
In essence, the ink-jet printing process involves digitized dot-matrix manipulation of drops of ink ejected from an ink-jet printhead onto an adjacent paper. The printhead generally consists of drop generator mechanisms and a number of columns of ink drop firing nozzles. Each column or selected subset (referred to in the art as a xe2x80x9cprimitivexe2x80x9d) of nozzles selectively fires ink droplets (typically each being only a few picoliters in liquid volume) that are used to create a predetermined print matrix of dots on the adjacently positioned paper as the pen is scanned across the media. A given nozzle of the printhead is used to address a given matrix column print position on the paper (referred to as a picture element, or xe2x80x9cpixelxe2x80x9d). Horizontal positions, matrix pixel rows, on the paper are addressed by repeatedly firing a given nozzle at matrix row print positions as the pen is scanned. Thus, a single sweep scan of the pen across the paper can print a swath of tens of thousands of dots. The paper is stepped to permit a series of contiguous swaths. Complex digital dot matrix manipulation is used to form alphanumeric characters, graphical images;, and even photographic reproductions from the ink drops.
In the state of the art, the nominal printhead-to-paper spacing is about one millimeter. Printer designers attempt to reduce pen-to-paper spacing as a means of improving print quality. However, carriage assembly torsional deflections can cause each printhead face, or xe2x80x9cnozzle plate,xe2x80x9d to be off-kilter, limiting the attempt to narrow the gap between the printhead and the paper. As illustrated in FIG. 2, a pitch angle of the printhead relative to the plane of the paper in the printing zone is referred to as theta-x (xcex8x), a roll angle is referred to as theta-y (xcex8y), and printhead yaw is referred to as theta-z (xcex8z). Any static or dynamic deflections during printing operations can result in dot placement errors and undesirable artifacts in the print.
Moreover, the problem becomes more complex when more pens are added to the printer design to accommodate higher print quality demands such as for very high resolution photographic reproductions where the ink-jet print is indistinguishable from a photolab darkroom developer process photograph, or multi-printhead, staggered, printhead array carriages for improving throughput. The larger the pen carriage, the greater the problem.
Most attempts to solve the problem focus on creating a more stable base platform for the hard copy apparatus as a whole. Such solutions often result in the use of heavier, more expensive, manufacturing materials or designs having a larger work space footprint.
Moreover, manufacturing tolerances allowed in springs, pen body datums, and the like parts of the assembly, can result in variations in torsional deflections in the carriage from assembly-to-assembly. Thus, another solution is required.
Other methods and apparatus are designed to stabilize the printhead alignment focus on the pen-to-bay interface mechanisms; see e.g., U.S. Pat. App. Ser. No. 08/878,489 by common assignee Williams, et al. for an INKJET PEN ALIGNMENT MECHANISM AND METHOD, or U.S. Pat. App. U.S. Ser. No. 09/431,712 by common assignor Williams, et al. for a DATUM STRUCTURE FOR COMPACT PRINT CARTRIDGE, or U.S. Pat. App. Ser. No. 09/431,711 by Heiles et al. for a UNITARY LATCHING DEVICE FOR SECURE POSITIONING OF PRINT CARTRIDGE(S) DURING PRINTING, PRIMING AND REPLENISHMENT (each assigned to the common assignee herein and incorporated herein by reference).
Therefore, there is a need for simplified mechanisms to reduce torsional deflections in ink-jet printhead carriage assemblies.
In its basic aspects, the present invention provides an ink-jet writing instrument carriage assembly for an ink-jet printer having a printing axis, a print media transport axis, and an ink drop firing axis, including: a carriage; a movable pen latch; a pen latch handle associated with the pen latch; and a biased handle retainer associated with the carriage, wherein the carriage and pen latch are each provided with complementary interfit devices such that when the movable pen latch is in a closed position with the retainer interlocked with the handle, the carriage and latch are held by the interfit devices with zero clearance interfit in at least one the axis such that torsional deflections of the carriage are thereby reduced.
In another basic aspect, the present invention provides an ink-jet writing instrument carriage assembly, including: a carriage for mounting at least one ink-jet printhead and for scanning across print medium positioned adjacently thereto such that the printhead is positioned with an ink drop nozzle side aligned for depositing ink drops on the print medium and a holddown side aligned for receiving a latching force; movable pen latch mechanisms for accessing the printhead mounted in the carriage when the latch mechanism is in an open position and for providing a force against a holddown side of the printhead when in a closed position; fixedly mounted to the carriage, latch retainer mechanisms for receiving the pen latch mechanisms via complementary interfit devices of each; mounted on the pen latch mechanisms, latch handle mechanisms for securing the pen latch mechanisms against the carriage and forcing a interfit between the complementary interfit device; and mounted on the carriage, biased handle retainer mechanisms for holding the latch handle mechanisms in the closed position, wherein the carriage and pen latch mechanisms complementary interfit devices provide pen pitch, pen roll and pen yaw counterforces when the pen latch mechanisms is in the closed position.
In another basic aspect, the present invention provides a method for reducing torsional deflections in an ink-jet writing-instrument carriage. The method includes the steps of : providing the carriage and writing-instrument latch with geometrically configured complementary interfit surfaces; and positioning the writing-instrument latch on the carriage against a bias such that when the writing-instrument latch is closed, counterforces to carriage torsional deflections which would affect the printhead-to-paper orientation and distance are established by the complementary interfit surfaces.
In another basic aspect, the present invention provides an ink-jet hard copy apparatus having a plurality of ink-jet writing-instrument for ejecting droplets of ink in a printing zone of the apparatus, the apparatus being defined by a scanning axis, a print media transport axis, and an ink drop firing axis, wherein the axes are mutually orthogonal, including: a writing-instrument carriage, mounted in the apparatus for selectively scanning the printing zone along parallel to the scanning axis, the carriage including a plurality of bays for locating the writing-instruments with respect to the printing zone; a movable writing-instrument latch having an open position for accessing the bays and a closed position for securing the writing instruments in the bays; a writing-instrument latch handle associated with the writing-instrument latch; and a biased handle retainer associated with the carriage, wherein the carriage and writing-instrument latch are each provided with complementary interfit devices such that when the movable writing-instrument latch in in the closed position with the retainer interlocked with the handle, the carriage and latch are held by the interfit devices with zero clearance interfit in at least one the axis such that torsional deflections of the carriage are thereby reduced.
Some of the advantage of the present invention are:
it reduces torsional deflections of a scanning ink-jet printhead carriage without resorting to heavier, more expensive manufacturing materials;
it is adaptable to a variety of implementations, including smaller footprint hard copy apparatus designs;
it provides a low cost manufacturing solution;
it provides a scalable design; and
it can reduce torsional deflections of the assembly by approximately an order of magnitude.
The foregoing summary and list of advantages is not intended by the inventors to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.